Sliding element having a layer system

Abstract

A sliding element which has a main body and a layer system which is applied thereto. The layer system has at least a first layer of the thickness s.sub.1, which is applied to the main body, and hard material particles having a mean extent d, which are introduced into the first layer and are therefore at least fixed on the main body. The thickness s.sub.1 of the first layer is such that it amounts to at least 60% and at most 90% of the mean extent d of the hard material particles, and the hard material particles form a surface structuring of the sliding element.

Claims

1. A sliding element comprising a main body and a coating layer system applied on the main body, the coating layer system comprising a first coating layer applied directly on the main body and having a thickness s.sub.1, and material particles introduced into the first coating layer with regions of the first coating layer being provided between material particles, wherein the material particles have a hardness greater than the hardness of the regions of the first coating layer provided between the material particles, the material particles have a mean extent d and are fixed on the main body, the thickness s.sub.1 of the first coating layer is from 60-90% of the mean extent d of the material particles and the material particles form a surface structuring of the sliding element.

2. The sliding element (1) according to claim 1, characterized in that at least part of the material particles protrudes beyond the first layer.

3. The sliding element according to claim 2, characterized in that the material particles are surrounded at most over an extent of 90% thereof.

4. The sliding element (1) according to claim 1, characterized in that the material particles are fixed on the main body in the form of a monolayer.

5. The sliding element according to claim 1, characterized in that the material particles have a substantially spherical shape.

6. The sliding element according to claim 1, characterized in that the material particles consist of silicon dioxide and/or boron carbide.

7. The sliding element according to claim 1, characterized in that the mean extent d of the material particles amounts to at least 1 m and at most 20 m.

8. The sliding element according to claim 1, characterized in that material particles are present over 10% to 50% of the surface of the layer system which is remote from the main body.

9. The sliding element according to claim 1, characterized in that the first layer is chemically deposited nickel.

10. The sliding element according to claim 1, characterized in that the surface of the layer system which is remote from the main body has recesses between the material particles and at least part of the recesses is spaced apart from neighboring material particles.

11. The sliding element according to claim 10, characterized in that the extent of the recesses is approximately equal to the mean extent d of the material particles.

12. The sliding element according to claim 10, characterized in that recesses are present over 10% to 50% of the surface of the layer system which is remote from the main body.

13. The sliding element according to claim 10, wherein a lubricant is provided in the recesses.

14. A sliding element comprising a main body and a coating layer system applied on the main body, the coating layer system comprising a first coating layer applied directly on the main body and having a thickness s.sub.1, a second coating layer having a thickness s.sub.2 applied on the first coating layer and material particles introduced into the first coating layer with regions of the first coating layer being provided between the material particles, wherein the material particles have a hardness greater than the hardness of the regions of the first coating layer provided between the material particles, the material particles have a mean extent d and are fixed on the main body, the combined thicknesses s.sub.1 and s.sub.2 of the first and second coating layers is from 60-90% of the mean extent d of the material particles and the material particles form a surface structuring of the sliding element.

15. The sliding element according to claim 14, characterized in that at least part of the material particles protrudes beyond the second layer.

16. The sliding element according to claim 14, characterized in that the thickness s.sub.1 of the first layer amounts to at least 10% and at most 30% of the mean extent d of the material particles.

17. The sliding element according to claim 14, characterized in that the second layer is a chemically deposited or electrodeposited layer, the hardness of which amounts to at least 80 HV 0.1 and at most 250 HV 0.1.

18. The sliding element according to claim 17, characterized in that further particles having a considerably smaller extent than the material particles are incorporated in the second layer.

Description

(1) Exemplary embodiments of the invention will be explained in more detail on the basis of the schematic drawings, in which:

(2) FIG. 1 shows a cross section through a sliding element having a layer system comprising hard material particles and a first layer,

(3) FIG. 2 shows a cross section through a sliding element having a layer system comprising hard material particles, a first layer and a second layer,

(4) FIG. 3 shows a cross section through a sliding element having a layer system comprising hard material particles, a recess, a first layer and a second layer.

(5) Mutually corresponding parts are provided with the same reference signs in all the figures.

(6) FIG. 1 schematically shows a cross section through a sliding element 1 according to the invention having a main body 11 and having a layer system 2. The layer system 2 comprises a first layer 21, in which hard material particles 3 are fixed and surrounded. The hard material particles 3 have a spherical shape and a uniform size. They form a monolayer and are located in the immediate vicinity of the surface of the main body 11. The thickness s.sub.1 of the first layer 21 amounts to approximately 75% of the diameter d of the hard material particles 3. Therefore, the hard material particles 3 have a protrusion 32 beyond the surface 25 of the layer system 2 which is remote from the main body 11. The protrusion 32 amounts to approximately 25% of the diameter d of the hard material particles 3. The first layer 21 can contain further particles.

(7) FIG. 2 schematically shows a cross section through a sliding element 1 according to the invention having a main body 11 and having a layer system 2. The layer system 2 comprises hard material particles 3, a first layer 21 and a second layer 22. The hard material particles 3 have a spherical shape and a uniform size. They form a monolayer and are located in the immediate vicinity of the surface of the main body 11. The hard material particles 3 are fixed on the surface of the main body 11 by the first layer 21. The thickness s.sub.1 of the first layer 21 amounts to approximately 20% of the diameter d of the hard material particles 3. The hard material particles 3 are surrounded by the second layer 22. The thickness s.sub.2 of the second layer 22 has been chosen in such a way that the hard material particles 3 are surrounded by the first layer 21 and the second layer 22 to an extent of approximately 75% of the diameter d thereof. Therefore, the hard material particles 3 have a protrusion 32 beyond the surface 25 of the layer system 2 which is remote from the main body 11. The protrusion 32 amounts to approximately 25% of the diameter of the hard material particles 3. The second layer 22 contains further particles 4, the size of which is considerably smaller than the diameter d of the hard material particles 3.

(8) FIG. 3 schematically shows a cross section through a sliding element 1 according to the invention having a main body 11 and having a layer system 2. As in the case of the sliding element 1 shown in FIG. 2, the layer system 2 shown in FIG. 3 comprises hard material particles 3, a first layer 21 and a second layer 22. In addition, a recess 5 is shown in the outer surface 25 of the layer system 2. The recess 5 is spaced apart from the neighboring hard material particles 3. As is shown, the first layer 21 already has a recess there. At this point, a hard material particle 3 is broke out of the first layer 21 after the application of the first layer 21 and before the application of the second layer 22. The second layer 22 was applied with a constant layer thickness 62, and therefore the recess formed by the hard material particle 3 breaking out in the first layer 21 is reproduced again on the surface of the second layer 22. The recess 5 can be seen in the height profile of the second layer 22.

(9) An embodiment as per FIG. 3 was investigated. Hard material particles 3 of silicon dioxide were fixed on a metallic main body 11 by means of a first layer 21 of chemically deposited nickel. The mean diameter of the silicon dioxide particles was 8 m. The thickness s.sub.1 of the fixing layer 21 was approximately 2 to 3 m. Investigations of the sample after this first coating step show that some of the silicon dioxide particles 3 have been lost after the application of the fixing layer 21. These particles left behind recesses of a corresponding size in the fixing layer 21. In a second coating step, the silicon dioxide particles 3 were surrounded by an electrodeposited copper layer 22. Furthermore, particles 4 of hexagonal boron nitride were dispersed in this layer. Investigations of the sample after the second coating step show that the recesses originally established in the fixing layer 21 were not leveled during the application of the surrounding layer 22, but rather can clearly be identified in the surface 25 of the surrounding layer 22. As a whole, the surface produced exhibits a copper layer 22 of coarse crystallinity comprising incorporated silicon dioxide particles 3 and a multiplicity of recesses 5. The occupation density of the silicon dioxide particles 3 amounts to between 4000 and 5000 particles per mm.sup.2. In further SEM investigations, particles 4 of hexagonal boron nitride were also detected on the surface.

(10) Tribological investigations designed as an endurance test were carried out on this sample. To simulate the run-in behavior, at the start of the test the loading of the frictional surface was increased gradually up to a contact pressure of 9.0 N/mm.sup.2. The sliding speed was 1 m/s and the operating temperature was 120 C. A comparative test was carried out with an uncoated plain bearing material. The samples were analyzed after a test duration of 6 hours.

(11) After completion of the run-in phase, the coated sample exhibits a coefficient of friction which lies approximately 25% to 30% below that of the uncoated plain bearing material. Furthermore, after the test this sample exhibits a clearly leveled surface comprising a multiplicity of recesses 5 having a diameter which is slightly smaller than the mean diameter of the silicon dioxide particles 3. The majority of the recesses 5 are at least partially filled. It is probable that the material which fills the recesses 5 is material removed from the surrounding layer, i.e. copper. It is striking that this material often has a porous structure in the recesses 5. The originally raised regions of the embedded silicon dioxide particles 3 have largely been removed after the test, and therefore the sliding element 1 has a leveled surface 25.

LIST OF REFERENCE SIGNS

(12) 1 Sliding element 11 Main body 2 Layer system 21 First layer 22 Second layer 25 Surface of the layer system 3 Hard material particles 32 Protrusion 4 Further particles 5 Recess